1. 3-5 Parallel Lines and Triangles

2. Parallel Postulate
Through a point not on a line, there is one and only one line parallel to the given line. There is exactly one line through P parallel to l

3. Triangle Angle-Sum Theorem
The sum of the measures of the angles of a triangle is 180

4. Problem 1: Using the Triangle Angle-Sum Theorem

5. Exterior angle of a polygon: an angle formed by a side and an extension of an adjacent side For each exterior angle of a triangle, the two non adjacent interior angles are its remote interior angles

6. Triangle Exterior Angle Theorem
The measure of each exterior angle of a triangle equals the sum of the measures of its two remote interior angles

7. Problem 3: Using the Triangle Exterior Angle Theorem

9. Problem 3: Applying the Triangle Theorems